1. Field of the Invention
This invention relates to a dental intra-oral X-ray photographing unit and more particularly to an X-ray photographing unit for exposing an X-ray film to imprint an image thereon by inserting the film into the mouth of a patient and irradiating X-rays from outside the mouth.
2. Prior Art
For example, an X-ray photographing unit for intra-oral use in dental treatment is under a restraint wherein a photograph is generally taken by inserting a film into the mouth of a patient. In such a device, the amount of X-ray irradiation is indirectly controlled by regulating the voltage and current of an X-ray tube and the period of time or irradiation. Accordingly, the result is that there is as a result of fluctuations in the voltage and the like of the X-ray tube, variations in the amount of irradiation. Accordingly, repetitive of photographing due to too large or too small of an amount of radiation to the film exposes a patient to overdoses of X-rays and makes it difficult to take X-ray photographs of the same quality.
Accordingly, in an effort to remove the disadvantages of the kind described above, the present inventors provided in their previous U.S. Pat. application Ser. No. 928,057 a system of determining the exact amount of X-rays to be irradiated not by regulating the tube voltage and the like but by detecting the X-ray amount actually irradiated and comparing the integrated value of the X-ray amount with an X-ray amount set point. This prior art was a system of controlling a normal X-ray amount on the basis of a purely electrical circuit device but there was no concrete reference made by the system to the problem of how to detect, in connection with the X-ray tube, the amount of electrical current corresponding to the X-ray amount to be a detection medium.